BIOL204 Cons Gen Session 1 Flashcards
What are the evolutionary processes that effect the genetic diversity of populations? (4)
- Mutation
- Selection
- Gene Flow
- Genetic Drift
Demographic Stochasticity
Fluctuations in Birth/Death rate, immigration/emigration, disease ect. This effects population size, small populations are more vulnerable to these changes
Genetic Load
A measure of the extent that average fitness, viability or other favourable attributes of a population is decreased by the factor under consideration (Encyclopedia of Genetics, 2001) SIMPLE: The reduction in beneficial genetic diversity after an event.
Frequency or Density dependent selection
Population growth rates are regulated by the density of . a population. POSITVIE= passanger pigeon, more individuals in flock increases foraging vision & opportunity, NEGATIVE= plants use up available nutrients in environment.
Directional Selection
One extreme of trait is selected against, leading to a shift in characteristics. eg. Giraffe necks
Directional selection is a type of natural selection in which the phenotype (the observable characteristics) of the species tends toward one extreme rather the mean phenotype or the opposite extreme phenotype. (look up graphs)
Disruptive or Diversifying Selection
Individuals with an intermediate trait are selected against- eg. some pollinators have a reduced preference to a medium plant height, produces polymorphic species traits
Stabilising or balancing selection
Extremes of a population are selected against, bell curve graph
Essential Reading
Frankham R (2005) Genetics and extinction. Biological Conservation 126(2), 131-140.
Frankham, R, Ballou JD and Briscoe DA (2010) Genetic consequences of small population sizes. Chapter 8 in Introduction to Conservation Genetics. 2nd Edn, Cambridge University Press.
Mills LS (2013) Genetic variation and fitness in wildlife populations Chapter 9 in Conservation of Wildlife Populations. 2nd Edn, John Wiley & Sons, Ltd
What is conservation genetics?
the use of genetic theory and techniques to reduce the risk of extinction in threatened species (frankham et al. 2004)
why can existing in a small population be a problem for organisms?
1) pops are more vulnerable to random fluctuations in birth, death, em or im. (demographic stochasticity)
2) There is reduced genetic diversity, so have lower adaptive potential and higher ‘genetic load’.
Give a definition of a mutation
A change in the DNA sequence or chromosome in the transmission of genetic information from parent to progeny
How can you measure mutation rates in organisms? (5)
per base per cell per organism per genome per generation
When thinking about the overall impact of mutation rate on genetic diversity, what should we note?
- There is variation in mutation rates between: bases, chromosomes, tissue types of multicellular organisms, sexes and species.
- In regions of the genome that code for proteins or that have other key function, the vast majority of mutations are immediately selected out of the population as they create a disadvantage to the organism: those individuals either die, or survive but are unable to breed.
- Quantifying mutation rates is an active and ongoing field of research investigating what the differences and what is driving those differences (Hodgkinson and Eyre-Walker, 2011)
What is the overall impact of mutation rate on genetic diversity?
From the perspective of evolutionary change in populations, it increases genetic diversity but at a relatively slow rate.
Define ‘Selection’
differential contribution of genotypes to the next generation due to differences in survival and reproduction.
Selection can either maintain or decrease the genetic diversity of populations: its effects are complex and often difficult to predict.
Define the heterozygote advantage or overdominance
heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype
Define the heterozygote disadvantage or underdominance
When the heterozygote has the lowest fitness
Explain genetic drift
A mechanism of evolution in which allele frequencies of a population change over generations due to chance (sampling error). Genetic drift occurs in all populations of non-infinite size, but its effects are strongest in small populations.
What is Gene flow?
the exchange of genetic information between demes through migration and subsequent breeding (a ‘deme’ = any local group of individuals that mate at random)
image in the lecture very helpful here! Gene flow between demes will maintain overall genetic diversity
what are the negative domino effects of being in a reducing population? (reducing due to human impact most likely)
1) pop is fragmented & reduced
2) gene flow is reduced dramatically
3) genetic drift increases & becomes stronger than selection
4) genetic diversity reduced
5) deleterious alleles increased, so more genetic load
6) less capacity for adaptation
7) inbreeding more likely = inbreeding depression
8) increased risk from demographic factors
The population is then vulnerable to complete collapse and extinction vortex.
Provide a case study regarding reduction in genetic diversity due to human impacts/genetic conservation
Genetic conservation techniques were used with the Californian condor (Gymogyps californianus). Due to human impact only 27 birds remained in 1987. They underwent a pop bottleneck & by this the deleterious allele for a lethal form of dwarfism increased in the pop, called chondrodystrophy. The birds were put into captivity and and the priority to to preserve genetic diversity. Reproduction in captivity was highly successful and by August 2002 the population consisted of 206 individuals divided into four subpopulations (Ralls and Ballou, 2004)
What is useful to know to inform conservation strategies? (4)
Genetic diversity present
Gene flow between pops
effective population size
extent of inbreeding
What is a Deme?
deme = any local group of individuals that mate at random
